Glasses in the SiOCN system produced by pyrolysis of polycyclic silazane/siloxane networks

In this work, polycyclic silazane/siloxane networks bearing SiO and SiN bonds were synthesized, via hydrosilylation reaction, from cyclotrisilazane, [CH2CH(CH3)SiNH]3, and cyclotetrasiloxane, [CH3(H)SiO]4, with different SiH:Sivinyl molar ratios. The resulting polymers were pyrolyzed up to 1000 °C, in N2 atmosphere, producing SiOCN glasses. The polymer-to-ceramic transformation was studied by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), and chemical analysis. The 1000–1500 °C, high temperature structural evolution was also studied using X-ray diffraction (XRD) and FTIR. The hydrosilylation reaction produced ethylenic bridge crosslinked polymeric precursors with good thermal stability. The SiOCN glasses obtained with ceramic yields higher than 80 wt% showed spectra absorptions of SiN, SiO, and SiC bonds in FTIR. The XRD patterns of the products obtained at 1500 °C displayed diffraction peaks characteristic of β-SiC and a broad halo centered at 22° (2θ), due to the amorphous silica phase. β-SiC diffraction peaks in the XRD patterns were more intense for the precursor richer in polysiloxane units, although absorptions of SiN, SiC, and SiO bonds were also observed in the FTIR spectra. Thus, the final materials were characterized as SiC/SiOCN composites in nano/amorphous phases.